// checking.c -- validation input
#include <stdbool.h>
#include <stdio.h>

// validate that input is an integer
long get_long(void);
// validate that range limits ate valid
bool bad_limits(long begin, long end, long low, long high);
// calculate the sum of the squares of integers
// a through b
double sum_squares(long a, long b);
int main(void) {
  const long MIN = -10000000L;  // lower limit to range
  const long MAX = +10000000L;  // upper limit to range
  long start;                   // start of range
  long stop;                    // end of range
  double answer;

  printf(
      "This program computes the sum of the squares of integers in a "
      "range.\nThe lower bound should not be less than -10000000 and\nthe "
      "upper bound should not be more than +10000000.\nEnter the limits (enter "
      "0 for both limits to quit):\nlower limits: ");
  start = get_long();
  printf("upper limits: ");
  stop = get_long();
  while (start != 0 || stop != 0) {
    if (bad_limits(start, stop, MIN, MAX))
      printf("Please try again.\n");
    else {
      answer = sum_squares(start, stop);
      printf("The sum of the squares of the integers from %ld to %ld is %g\n",
             start, stop, answer);
    }
    printf("Enter the limits (enter 0 for both limits to quit):\n");
    printf("lower limit: ");
    start = get_long();
    printf("upper limit: ");
    stop = get_long();
  }
  printf("Done.\n");

  return 0;
}

long get_long(void) {
  long input;
  char ch;

  while (scanf("%ld", &input) != 1) {
    while ((ch = getchar()) != '\n') putchar(ch);  // dispose of bad input
    printf(
        " is not an integer.\nPlease enter an integer value, such as 25, -178, "
        "or 3: ");
  }

  return input;
}

double sum_squares(long a, long b) {
  double total = 0;
  long i;

  for (i = a; i <= b; i++) total += (double)i * (double)i;

  return total;
}

bool bad_limits(long begin, long end, long low, long high) {
  bool not_good = false;

  if (begin > end) {
    printf("%ld isn't smaller than %ld.\n", begin, end);
    not_good = true;
  }
  if (begin < low || end < low) {
    printf("Values must be %ld or greater.\n", low);
    not_good = true;
  }
  if (begin > high || end > high) {
    printf("Values must be %ld or less.\n", high);
    not_good = true;
  }

  return not_good;
}
